The present invention relates to chemical assays, particularly immunoassays, for detecting Chlamydia trachomatis. More particularly, the invention concerns means for assessing the adequacy of a cellular test specimen to be assayed, specifically a cervical or urethral specimen.
Chlamydia trachomatis is a Gram-negative bacterium responsible for a number of disease manifestations in humans including trachoma, non-gonococcal urethritis, cervical infections and lymphogranuloma venereum. The development of extremely sensitive methods for the detection of Chlamydial infections is medically important since the organism is often harbored without obvious symptoms of infection.
Due to the obligate intracellular nature of its life cycle, the accurate detection of Chlamydia requires that the host cells in which the organism replicates be carefully sampled. In the case of genital, cervical and ocular infections, the participating host cells are the columnar epithelial cells [Kuo, C.-C. (1988) Host Response. In, Microbiology of Chlamydia, ed. A. L. Barron, CRC Press, Inc., Boca Raton, Fla., USA]. Columnar epithelial cells constitute a broad class of cell type found, among other places, in the mucus membranes lining the eye, urethral and portions of the female reproductive tract, including the cervix. The cells display a characteristic morphology that allow the trained individual to differentiate these cells from other cell types when observing a specimen under a microscope. Thus, the detection of C. trachomatis by staining under a microscope offers the opportunity to an individual performing the test to observe if an adequate number of columnar epithelial cells are present in the specimen.
Procedures for obtaining adequate sample collection for accurate testing for Chlamydia have been described in detail [Smith, T. F. and L. A. Weed (1983), Evaluation of Calcium Alginate-tipped Aluminum Swabs Transported in Culturettes Containing Ampules of 2-Sucrose Phosphate Medium for Recovery of Chlamydia trachomatis. Am. J. Clin. Pathol. 80:213-215; Embil, JA., Thiebaux, J., Manuel, F. R., Pereira, L. H. and S. MacDonald (1983), Sequential Cervical Specimens and the Isolation of Chlamydia trachomatis: Factors Affecting Detection. Sex. Trans. Dis. 10:62-66; and Singal, S. S., Reichman, R. C., Graman, P. S., Griesberger, C, Trupei, M. A. and Menegus, M. A. (1986), Isolation of Chlamydia trachomatis from Men with Urethritis: Relative Value of One vs. Two Swabs and Influence of Concomitant Gonococcal Infection. Sex. Trans. Dis. 13:50-52]. These procedures include specifications as to the composition of the swab to be used for the sampling, how the swab is actually deployed during the sampling process and how it is subsequently processed. Variations in any of these steps can, however, significantly alter the performance of the diagnostic assay. Furthermore, failure to collect a sample from the anatomical site at which these cells are located also can result in a false-negative test. Unfortunately, those responsible for collecting a proper sample, even highly-trained medical staff, do not always follow or appreciate the procedures specified for adequate collection of a specimen.
Recently, rapid immunoassay test devices have been devised which permit essentially untrained individuals to perform qualitatively determinations for the presence of a variety of clinically significant antigens and antibodies in biological specimens such as urine and swabs. Examples of such devices are described in U.S. Pat. Nos. 4,623,461 and 4,632,901 and in European Patent Publication Nos. 186,100 and 217,403. A rapid immunoassay test device specifically designed for the detection of Chlamydia is described in European Patent Publication No. 264,036.
The detection of Chlamydia by immunoassay is based on the binding of antigens present in Chlamydia cells by antibody raised to be specific to such antigens, and the ability to detect such binding, such as by the formation of an instrument readable or visually observable signal. In these assays, the test specimen is subjected to conditions to disrupt cellular material in order to expose detectable Chlamydia markers. In the process, therefore, the individual performing the test loses the ability to examine the disrupted sample for adequacy of epithelial cells collected. Currently, such immunoassays do not include any procedure or control to determine whether or not the sample taken from the patient is an adequate one, thus the risk of false-negative results can be significant. Because Chlamydia is present within infected cells, a negative test result can be due to the inadequacy of the sample collected rather than on the absence of Chlamydial infection.